Heat applied electrochemical cell separator

Abstract

A separator for a bobbin-style electrochemical cell is inserted into an interior opening within a ring-shaped cathode in an electrochemical cell can. An expansion force is then applied to an interior surface of the separator to press the separator against the interior walls of the cathode. A tool may then remove various creases and/or wrinkles in the separator and/or may then heat seal at least a portion of the tubular walls of the separator to minimize the void space between the separator and active material (e.g., cathode and/or anode) within the electrochemical cell.

That which is claimed: 
     
       1. An electrochemical cell comprising:
 a container; 
 a ring-shaped cathode disposed within the container wherein the cathode includes an exterior surface in contact with the container and an interior surface surrounding a hollow interior; 
 an anode disposed within the hollow interior of the cathode; and 
 a separator positioned between the cathode and the anode, 
 wherein the separator has a tubular sidewall and a closed bottom end, 
 wherein the tubular sidewall has at least one overlapping portion defined by at least two layers of a separator sheet being positioned between the cathode and the anode, 
 wherein at least a portion of the separator is steamed while in place adjacent to the interior surface of the ring-shaped cathode, and 
 wherein at least part of the overlapping portion is heat sealed after the at least a portion of the separator is steamed, such that the at least two layers are bonded relative to one another. 
 
     
     
       2. The electrochemical cell of  claim 1 , wherein the separator is a nonwoven fibrous separator. 
     
     
       3. The electrochemical cell of  claim 2 , wherein the nonwoven fibrous separator comprises thermoplastic fibers and wherein portions of the thermoplastic fibers positioned within at least part of the overlapping portions are melt-bonded relative to one another. 
     
     
       4. The electrochemical cell of  claim 1 , wherein the separator sheet is ion permeable. 
     
     
       5. The electrochemical cell of  claim 4 , wherein the overlapping portions of the separator sheet are ion permeable. 
     
     
       6. The electrochemical cell of  claim 1 , wherein the separator is a convolute separator comprising a spirally wound separator sheet and having a first end and a second end, and wherein the first end overlaps the second end to form an overlapping portion. 
     
     
       7. The electrochemical cell of  claim 1 , wherein at least a portion of the closed bottom end is heat sealed. 
     
     
       8. The electrochemical cell of  claim 7 , wherein the closed bottom end of the separator is ion permeable. 
     
     
       9. The electrochemical cell of  claim 1 , wherein the separator has an open top opposite the closed bottom end, and wherein the heat seal extends between the open top and the closed bottom end. 
     
     
       10. The electrochemical cell of  claim 1 , wherein the separator is radially pressed against the interior surface of the cathode.